1. Field of the Invention
This invention relates to lacrimal silicone stents and a method of inserting the same, and more particularly, to asymmetric lacrimal silicone stents having a very large diameter segment which is inserted transnasally.
2. Description of the Prior Art
The lacrimal gland produces the aqueous layer of the tear film. The orbital portion of the lacrimal gland is located in the superior temporal orbit. Ductules from the main lacrimal gland pass through the adjacent palpebral lacrimal gland to empty in the superior conjunctival cul-de-sac which is on the posterior surface of the superior upper lid. Accessory lacrimal glands in the upper and lower lids also contribute to tear production.
The tears bathe the eye and then flow into the upper and lower puncta, which are located on the medial upper and lower lid margins. The tears then drain through the superior and inferior canaliculi, common canaliculus, lacrimal sac, and down the nasolacrimal duct into the nose. The nasolacrimal duct can become obstructed either congenitally or as an acquired obstruction in adulthood. When the nasolacrimal duct becomes obstructed, tears can no longer drain from the surface of the eye through the lacrimal system into the nose. The tears therefore well up over the eyes and spill over the lids onto the face. The patient has to constantly dab the eyes with a tissue. In addition, tears stagnate in the lacrimal sac which allows bacteria to multiply. The lacrimal sac then becomes infected (dacryocystitis). Dacryocystitis causes the lacrimal sac to become swollen, red and painful. Pus exudes from the lacrimal sac through the canaliculi onto the eye. This results in purulent material constantly covering the eye. In time, the dacryocystitis does not respond to antibiotics and surgery becomes necessary.
Dacryocystorhinostomy (DCR) is the surgery used to correct nasolacrimal duct obstruction. In a DCR, a new opening (ostium) is created between the lacrimal sac and the nose. This allows tears to flow from the lacrimal sac through the DCR ostium into the nose. An open or incisional DCR requires an incision on the side of the nose. In an open DCR, a large DCR ostium is created by making a 17 mm. plus opening in mucosa and bone. This procedure has significant morbidity, a prolonged recovery, and the threat of scarring and hemorrhage. In contrast, a transnasal endoscopic DCR has must less morbidity, no incision, and a quick recovery time. An endoscope DCR may be performed using lacrimal or sinus surgery instruments, a laser, or a balloon catheter. The endoscopic DCR ostium is smaller (5 to 9 mm.) than that of an open DCR. Because the DCR ostium is only 5 to 9 mm. (0.1969 to 0.354 inch) in diameter, a stent is required to keep the DCR ostium open after surgery. Otherwise postoperative inflammation and scarring may cause it to close.
In selecting a stent for this purpose, it is necessary to keep in mind the dimensions and properties of the canaliculi which are the narrowest part of the lacrimal system, as well as the properties of the silicone stent material and the technique for inserting the stent. An adult patient has canaliculi which are about 0.5 mm. (0.01969 inch) in diameter. It is possible however, to employ silicone tube stents which are somewhat larger in outer diameter, because there is a certain amount of resiliency, and give, in the tissue, and because tubular silicone stents tend to become thinner when placed under tension as they are pulled through the lacrimal system. The size of the silicone stent which can be used reaches an upper limit for the largest diameter stent which can be pulled through the canaliculi readily and without damaging the canaliculi. I have found that the largest diameter stent which can be so used is 0.053 inch.
It has been proposed in the prior art to use a silicone tube stent with a uniform diameter of 0.020 inch. However, this is too small a diameter to keep the endoscopic DCR ostium open.
A larger diameter tube with a diameter of 0.037 inch has also been used in the prior art. This larger diameter tube is still too small and soft to stent the balloon DCR ostium. Furthermore, the larger diameter causes irritation and epithelial defects on the cornea and conjunctiva where the tube lays against the eye in the medial canthus. It may also obstruct the drainage through the tiny canaliculi. The silicone tube comes with an attached rigid metal probe on each end. To place the tube in the lacrimal system, the probe is pushed through the punctum, canaliculus, lacrimal sac, DCR ostium into the nose. The probe is grasped in the nose and pulled down the nose and out the external naris. The probe pulls the attached silicone tube through the punctum, canaliculus, lacrimal sac and DCR ostium into the nose. The opposite end of the tube with its attached probe is brought through the opposing punctum and canaliculus, the lacrimal sac, and the DCR ostium into the nose. The probe attached to the opposite end is grasped in the nose and brought down the nose and out the external naris. The probe pulls the attached silicone tube through the punctum, canaliculus, lacrimal sac, and DCR ostium into the nose. The two ends of the tube are then cut 11/2 cm. inside the external naris. The tube is left in place for about six months.
In an effort to stent the endoscopic DCR ostium with a larger diameter stent, which is too large to pass through the canaliculi, a short, more rigid stent, which can be placed from the nasal cavity, has been proposed. The short, large diameter stent is pushed from inside the nose through the endoscopic DCR ostium into the lacrimal sac. When in place, the stent extends from the lacrimal sac through the endoscopic DCR ostium into the nose. A number of such stents have been tried. They have had several problems. They are difficult or impossible to push into place. They frequently fall out shortly after surgery. Attempts to fixate them on a silicone tube are only minimally helpful. These stents can induce inflammation, infection and scarring.
I previously designed a "fat" silicone tube that has a large diameter in the portion that stents a balloon DCR ostium. An example is shown in my copending application Ser. No. 08/547,792, filed Oct. 25, 1995. It has a small diameter in the segment that lies against the eye. The large diameter portion (usually 0.052 inch in diameter) cannot be pulled through the small diameter puncta and canaliculi without slipping off the probe. Therefore, each end of the tube has a long small diameter portion. The small diameter ends of the tube are attached to the probe. After the probe is grasped in the nose, it is pulled down the nose and pulls the attached small diameter end of the tube through the puncta, canaliculi, lacrimal sac, balloon DCR ostium into the nose. The small diameter end of the tube is then grasped in the nose. As the small diameter segment is pulled down the nose, it pulls the attached larger diameter portion of the tube through the narrow puncta and canaliculi, the larger lacrimal sac and DCR ostium into the nose. This is done with each end of the tube. When in place, the ends of the tube are cut 11/2 cm. inside the external naris. The larger diameter segment of the tube will lie in the distal canaliculi, lacrimal sac, and balloon DCR ostium extending into the nose. The small diameter end of the tube will have been cut off.
However, there are two problems with this "fat" tube. In some patients it can be difficult to pull the large diameter segments through the canaliculi. If the canaliculi are somewhat narrow, the tubes may break when the surgeon exerts traction on the narrow distal segment in the nose in an attempt to pull the fat segment through the canaliculi into the lacrimal sac. A second problem is that pulling the large diameter segments through the canaliculi may stretch the canaliculi enough to damage them and cause fibrosis (scarring). In this case, the canaliculi will become stenotic (narrow) and obstruct tear drainage after the tube is removed. This results in tearing. In addition, a tube with a diameter larger than 0.053 inch is needed to stent the balloon DCR ostium in some cases. However, as has been explained, it is impossible to pull a tube with a diameter much larger than 0.053 inch through the canaliculi into the lacrimal sac.
If a silicone tube could be brought into the canaliculi from the nasal cavity, a much larger diameter tube could be used. However, during surgery, it is usually not possible to see the common canaliculus from inside the nose, even when viewed through an endoscope. It is certainly not possible to thread a silicone tube from the nose through the tiny common canaliculus. For this reason, silicone intubation from the nose through the lacrimal sac into the canaliculi has never been performed.
An early proposal to insert a large canula into the lacrimal system is shown in U.S. Pat. No. 2,154,968. This patent suggests the use of a spiral canula of thin metal wire, the external diameter of which may vary up to 5/32 of an inch. The spiral is tapered at one end to facilitate insertion into the lacrimal duct. A tube is inserted through the punctum, canaliculus, lacrimal sac, and nasolacrimal duct into the nasal cavity, and a wire is threaded through the tube. The end of the wire is pulled out the nostril and the spiral canula is threaded on the wire with its tapered end turned upward. A supporting sleeve is placed on the wire and the canula is drawn up into the nasolacrimal duct from the nasal cavity.
However, the canula of the U.S. Pat. No. 2,154,968 is not a stent; it is a conduit. It is made of hard metal, not from silicone. The canula is not placed in an ostium surgically created to drain tears to the nasal cavity. In fact, the proposal is not clinically viable. It would lead to chronic infection and damage and the duct would close up after removal of the spiral canula. Moreover, the procedure suggested in the U.S. Pat. No. 2,154,968 would be very difficult for a surgeon to perform. For example, the surgeon would not be able to see that the canula is properly positioned, because visualization of the nasolacrmal duct is blocked by the inferior turbinate.
U.S. Pat. No. 5,437,625 discloses a device for intubation in the form of a single flexible silicone tube including a central thinner soft segment and a pair of larger diameter end segments with free ends which are sharp-pointed and sealed closed. The end segments have an outer diameter of 0.5-0.7 mm. (0.0197-0.0276 inch). The end segments have small cuts which receive metal probes extending to the closed tips during intubation. It has been found that the sharp-pointed end of the end segments, being rigid and hard, traumatize, and are too damaging to the canaliculi.
U.S. Pat. No. 4,305,395 teaches the use of metal probes inserted through openings in the side walls of polyamide tubular sheaths attached to the ends of a length of silicone rubber tubing. The tips of the probes abut the closed distal ends of the tubular sheaths. The tubing is then positioned in the lacrimal system by passing the probes inserted in the sheaths through the lacrimal system from above into the nose. The probes are removed, and the sheaths are grasped and pulled to position the tubing in the lacrimal system.
U.S. Pat. No. 4,380,239 is another example of the use of probes for the intubation of a silicone rubber tube. The probes, which are formed of steel wire, are inserted into the open end of the tube to facilitate insertion of the tube though a canaliculus into the lacrimal duct.
In the methods of the U.S. Pat. Nos. 4,305,395 and 4,380,239, the sheaths or probes must be pulled from the nostril, and during the procedure epistaxis and bone fracture of the inferior nasal concha sometimes occurs.
The silicone lacrimal stents of the prior art are tubular. Because a tube can only be manufactured by a molding process when the entire tube is of uniform diameter, a tube with a variable diameter can only be made by an extrusion process. The less reliable extrusion process allows tubes to be made when the variation in outside diameter is minimal. However, extrusion alone is not a feasible process where, as in the present invention, there is a large variation in the diameter of stent segments. Moreover, tubular extruded stents have a surface which is rougher than the surface possible from a molded stent. The extrusion process is also costly, because a significant percentage of extruded tubes do not conform to the specified diameter and must be discarded.